Electrostatic motor

ABSTRACT

An electrostatic motor has a disc-shaped stator and a disc-shaped rotor are opposed to each other in a vacuum container. In the stator, first and second electrodes, which are attached to electrode supports, and which are electrically insulated from each other by an insulator, are arranged alternately in the circumferential direction. The first electrodes and the second electrodes on the side of the stator are arranged at a spacing of two or more rows at a predetermined distance from the center of a rotating shaft. The first electrodes and the second electrodes are arranged at a predetermined distance from the center of the rotating shaft and at an intermediate position between the rows of the first and second electrodes on the side of the stator.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.12/308,366, filed May 6, 2009, which is a National Stage application ofPCT/JP2007/061546, filed Jun. 7, 2007, the entireties of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

I. Technical Field

The present invention relates to an electrostatic motor thatrotationally drives using electrostatic force, and in particular to anelectrostatic motor that rotationally drives by generating a highelectric field in a vacuum.

II. Background Art

Most conventional electric motors use electromagnetic force generated bya coil and magnet. Electrostatic motors that rotationally drive usingelectrostatic force are also known (e.g., Japanese Patent ApplicationLaid-Open No. 8-88984, and Study of Servo System using ElectrostaticMotors written by Akio Yamamoto et al.)

However, conventional electric motors using electromagnetic forcegenerated by a coil and magnet produce gas in a vacuum, breaking up thevacuum. In addition, since conventional electric motors use magneticmaterials, they cannot be operated in strong magnetic fields.

Conventional electrostatic motors, as described above, also produce gasin a vacuum, breaking up the vacuum. In conventional electrostaticmotors, the electric field is increased by placing a large number ofpairs of electrodes on an insulator so that the electrodes are closelyspaced. However, this method is prone to dielectric breakdown, creepingdischarge, spark discharge, and other concerns. Accordingly, a strongelectric field cannot be generated, and sufficient driving force cannotbe produced. Therefore, practical electrostatic motors have not yet beenrealized.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing drawbacks.Accordingly, an object of this invention is to provide an electrostaticmotor that generates a strong electric field in a vacuum so that it canrotationally drive with sufficient driving force.

Another object of the present invention is to provide an electrostaticmotor designed so as to prevent dielectric breakdown, creepingdischarge, spark discharge, and the like to operate in a strong electricfield, and also to be lightweight.

In order to solve the foregoing problems, an electrostatic motoraccording the present invention has the characteristics described below.

A first aspect of the invention is an electrostatic motor characterizedin that a disc-shaped stator and a disc-shaped rotor are disposedopposite each other in a vacuum container such that the stator is fixedto the main body of the vacuum container and the rotor is pivotallysupported on the main body of the vacuum container so as to freelyrotate via a rotating shaft; the stator has first electrodes and secondelectrodes electrically insulated by an insulator and attached toelectrode supports so as to alternate along the circumferences of theelectrode supports; the rotor has first electrodes and second electrodeselectrically insulated by an insulator and attached to electrodesupports so as to alternate along the circumferences of the electrodesupports; the first and second electrodes on the stator side are eacharranged at a spacing of two or more rows at a predetermined distancefrom the center of the rotating shaft; the first and second electrodeson the rotor side are each arranged at a predetermined distance from thecenter of the rotating shaft, and intermediate between the rows of thefirst and second electrodes on the stator side; predetermined electricfields are applied to the first and second electrodes on the statorside; and

voltages of different polarities are applied to the first and secondelectrodes on the rotor side so as to be switched according topredetermined timing.

A second aspect of the invention is the electrostatic motor of the firstaspect described above, characterized in that the first and secondelectrodes on the stator side and the first and second electrodes on therotor side are each pin-shaped and are each arranged parallel to theaxial direction of the rotating shaft.

A third aspect of the invention is the electrostatic motor of the firstor second aspect described above, characterized in that the electrodesupports of the first and second electrodes on the stator side, and theelectrode supports of the first and second electrodes on the rotor sideare insulatively supported by the insulators respectively so as to allowsufficient creepage distance.

A fourth aspect of the invention is the electrostatic motor of any oneof the first to third aspects described above, characterized in that theinsulators on the stator side and the rotor side each have one or aplurality of grooves formed thereon.

A fifth aspect of the invention is the electrostatic motor of any one ofthe first to fourth aspects described above, characterized in that theends of the first and second electrodes on the stator side and the endsof the first and second electrodes on the rotor side are round in shape.

A sixth aspect of the invention is the electrostatic motor of any one ofthe first to fifth aspects described above, characterized in thatstainless steel is used for metallic components disposed in the vacuumcontainer and inorganic insulator is used as insulating components.

A seventh aspect of the invention is the electrostatic motor of any oneof the first to sixth aspects described above, characterized in that anonmagnetic material is used as the metallic components disposed in thevacuum container.

An eighth aspect of the invention is the electrostatic motor of any oneof the first to seventh aspects described above, comprising an encoderincluding a slit plate and a sensor that detect the relative positionbetween the first and second electrodes on the stator side and the firstand second electrodes on the rotor side.

A ninth aspect of the invention is the electrostatic motor of any one ofthe first to eighth aspects described above, characterized in that agas-absorbing material is deposited on components disposed in the vacuumcontainer.

The present invention adopts the foregoing configuration in which thefirst and second electrodes attached to the electrode supports of thestator and the rotor are located within the vacuum. Accordingly, unlikea conventional electrostatic motor in which groups of electrodes aresupported by an insulator or insulators, the present invention preventsdielectric breakdown even if there is a strong electric field betweenthe electrodes. This results in output as high as or higher than thatobtained by an electromagnetic motor. Accordingly, an electrostaticmotor that generates a strong electric field in the vacuum such that itcan rotationally drive with sufficient driving force can be provided. Anelectrostatic motor that can drive in a high, clean vacuum isapplicable, for example, in semiconductor manufacturing apparatuses. Inaddition, the electrostatic motor is free from windage loss, thusoffering improved efficiency. Moreover, an electrostatic motor thatdrives in a strong electric field generated between the electrodesallows practical applications including small or large motors, andachieves high output and weight reduction.

In the present invention, the electrode supports are insulativelysupported and grooves are formed in the insulator, allowing sufficientdistance for creepage. Accordingly, an electrostatic motor effectivelyprevents dielectric breakdown, creeping discharge, spark discharge, andother concerns, and generates a strong electric field.

Additionally, in the electrostatic motor according to the presentinvention, a stainless steel etc. or an inorganic insulator that produceless residual gas, such as porcelain or glass, are used as components.Therefore, the electrostatic motor can be used in the clean vacuum.Further, using a nonmagnetic material as a metallic components resultsin a nonmagnetic motor, which can be used in a strong magnetic field.

Furthermore, the electrostatic motor according to the present inventionuses no heavy magnetic materials as metallic components and is thereforelighter in weight than conventional ones.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a vertical section of an electrostatic motor according tothe first embodiment of the present invention;

FIG. 2 is a plan view of a stator in the first embodiment;

FIG. 3 is a plan view of a rotor in the first embodiment;

FIG. 4 is a partially-detailed schematic view of first and secondelectrodes of the stator in the first embodiment;

FIG. 5(A) is a development vertical partial view of electrode supportsand first and second electrodes on the stator side in the firstembodiment;

FIG. 5(B) is a development vertical partial view of the electrodesupports and first and second electrodes on the rotor side in the firstembodiment;

FIG. 6 illustrates the principle of action of the first and secondelectrodes on the stator side and the first and second electrodes on therotor side in the first embodiment;

FIG. 7 shows the voltage waveforms of the first and second electrodes onthe rotor side in the first embodiment;

FIG. 8 shows a vertical section of an electrostatic motor according tothe second embodiment;

FIG. 9 shows a vertical section of an electrostatic motor according tothe third embodiment;

FIG. 10 shows a vertical section of an electrostatic motor according tothe fourth embodiment, in which first and second electrodes on thestator side and first and second electrodes on the rotor side areradially arranged with respect to the center of a rotating shaft;

FIG. 11 is a sectional view of the stator in the fourth embodiment; and

FIG. 12 is a sectional view of the rotor in the fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of an electrostatic motor according to the present inventionwill be described in detail hereinafter.

FIG. 1 shows a vertical section of an electrostatic motor according tothe first embodiment of the present invention. FIG. 2 is a plan view ofa stator in the first embodiment, and FIG. 3 is a plan view of a rotorin the first embodiment. FIG. 4 is a partially-detailed schematic viewof the first and second electrodes of the stator in the firstembodiment.

In an electrostatic motor according to the first embodiment, disc-shapedstator S and disc-shaped rotor R are disposed opposite to each other invacuum container 11, and stator S is fixed to the main body of thevacuum container 11. The electrostatic motor in the first embodiment isoperable in the vacuum of 3 Pa or less.

In the electrostatic motor in this embodiment, first electrodes 34A arefixed to electrode supports 31 on the stator S side. The firstelectrodes 34A are arranged in two rows at a predetermined distance fromthe center of rotating shaft 1 (i.e., the center of motor base 10).Similarly, second electrodes 34B are fixed to other electrode supports32 on the stator S side. As shown in FIGS. 2 and 4, the first electrodes34A and the second electrodes 34B are arranged so as to alternate. Thefirst and second electrodes 34A, 34B are disposed along thecircumferences of the electrode substrates 31, 32 respectively atregular intervals parallel to the rotating shaft 1 such that the firstand second electrodes 34A, 34B are radially fixed in two rows. Theelectrode supports 31, 32 with the first and second electrodes 34A, 34Brespectively are fixed on an insulator 33, which is mounted on the motorbase 10 (i.e., the main body of the vacuum container 11). The insulator33 provides sufficient insulating thickness and creepage distance, andhas a plurality of grooves formed to prevent creeping discharge. Here,sufficient insulating thickness should be equal to or greater than thebreakdown voltage of the insulator, and sufficient creepage distance isseveral times or more larger than this thickness. The number of grooves,groove shape, groove depth, and other characteristics, may be set asneeded according to the size and application of the electrostatic motor.

On the other hand, a first electrode 44A is fixed to each electrodesupports 41 on the rotor R side. These first electrodes 44A are arrangedin one row at a predetermined distance from the center of the rotatingshaft 1. Also, disposed on each of the other electrode supports 42, onthe rotor R side is a second electrode 44B. As shown in FIG. 3, thefirst electrodes 44A and the second electrodes 44B are arranged so as toalternate like those on the stator S side. The first and secondelectrodes 44A, 44B are disposed along the circumferences of theelectrode supports 41, 42 respectively at regular intervals parallel tothe rotating shaft 1 such that the first and second electrodes 44A, 44Bare radially fixed in one row. The electrode supports 41, 42 with thefirst and second electrodes 44A, 44B respectively are fixed on aninsulator 43, which is mounted on the rotating shaft 1. As on the statorS side, the insulator 43 provides sufficient insulating thickness andcreepage distance, and has a plurality of grooves formed to preventcreeping discharge. The number of grooves, groove shape, groove depth,and other characteristics may be set as needed according to the size andapplication of the electrostatic motor.

As described above, the first and second electrodes 44A, 44B on therotor R side are fixed on the supports 41, 42 respectively at regularintervals parallel to the rotating shaft 1, like the first and secondelectrodes 34A, 34B on the stator S side. However, as shown in FIG. 1,the positions of the first and second electrodes 44A, 44B on the rotor Rside from the center of the rotating shaft 1 are in the middle of therows of the first and second electrodes 34A and 34B on the stator S sideso that the rotor R is rotationally drivable. The first electrode 34A,second electrode 34B, first electrode 44A and second electrode 44B arepin-shaped. It is preferable that the ends of the electrodes are roundin order to prevent discharge between them. The shape of theseelectrodes, however, is not limited to pin-shape.

Power is supplied to the electrodes 44A, 44B on the rotor R side throughslip rings 51, 52 and brushes 61, 62.

An encoder is composed by adopting an optical system (i.e., a slit plate7 and a sensor 8) or a magnetic system (i.e., a magnetic disc and asensor). In this embodiment, the former is used. The timing of thesupply of power to the first and second electrodes 44A, 44B on the rotorR side is detected by the sensor 8, and the detected result is subjectedto signal processing by a drive circuit (not shown). A high voltage(approximately 1 to 100 kV) is outputted and supplied to the first andsecond electrodes 44A, 44B.

When the electrostatic motor is used in air or gas, a vacuum seal 9 isattached to the motor base 10 in order to maintain the vacuum within theelectrostatic motor.

The present invention uses an electrostatic motor that operates in thevacuum. The present invention, needless to say, functions as anelectrostatic motor even in insulation gas such as SF6 gas.

In the description above, the first and second electrodes 34A and 34 brespectively on the stator S side are arranged in two rows, whereas thefirst and second electrodes 44A and 44 b respectively on the rotor Rside are arranged in one row. However, as described below, the number ofrows is not limited to only one, as two or more rows may also be set.

Additionally, in the first embodiment, stainless steel or the like thatproduce less residual gas may be used as metallic components that areplaced in the vacuum container 11 (e.g., the first and second electrodes34A, 34B, electrode supports 31, 32, first and second electrodes 44A,44B, and electrode supports 41, 42). Also, an inorganic insulator suchas porcelain or glass, which produces less residual gas, may be used asan insulating components. The usability of the electrostatic motor inthe clean vacuum can thereby be ensured. It is also effective to deposita gas absorbing material (i.e., gettering substance), such as titanium,vanadium, tantalum, or zirconium, on components used in the vacuumcontainer 11.

In the first embodiment, using a nonmagnetic material as the metalliccomponents used in the vacuum container 11 enables a nonmagnetic motorthat can be used in a strong magnetic field. Additionally, no heavymagnetic material is used as the metallic components, thus contributingto weight reduction as well.

The principles of operation of the electrostatic motor according to thefirst embodiment, which has the foregoing configuration, will now beexplained. As shown in FIG. 5(A), by applying a high voltage(approximately 1 to 100 kV) between the electrode supports 31, 32 on thestator S side, a high electric field (1 to 100 kV/mm or so) is generatedbetween the first and second electrodes 34A, 34B.

Since the electrostatic motor is configured so that the first and secondelectrodes 44A, 44B on the rotor R side freely move along thecircumference between the first and second electrodes 34A, 34B on thestator S side, the first and second electrodes 44B, 44A are positivelyand negatively charged respectively by applying a high positive voltage(1 to 100 kV or so) to the electrode supports 42. In terms of chargetiming, the direction of thrust (i.e., rotating force) is, for example,determined by where the electrodes 44B on the rotor R side are locatedrelative to the second electrodes 34B on the stator S side. Therefore,the magnitude and time of the voltage greatly affect the magnitude ofthe thrust (rotating force).

FIG. 6 illustrates the principle of the action of the electrostaticmotor by showing only the first and second electrodes 34A, 34B on thestator S side and the first and second electrodes 44A, 44B on the rotorR side. For instance, when each of the second electrodes 44B on therotor R side has reached a location (i.e., location X1) that is slightlyto the right of the location X0 of the second electrode 34B on thestator S side, a positive potential is applied to the second electrode44B. Thereby, repulsion force occurs between the second electrodes 34Band the second electrode 44B, whereas attractive force occurs betweenthe first electrodes 34A and the second electrode 44B. Consequently, therotor R connected to the first and second electrodes 44A, 44B is subjectto a driving force toward the right and moves accordingly.

The voltage of each of the second electrodes 44B switches to a location(i.e., location X2) that is immediately before first electrodes 34A.Second electrode 44B repeats this switching operation each time thepositional timing of the second electrode 44B is detected by the signalof the encoder sensor 8.

FIG. 7 shows the voltage waveforms of the first and second electrodes44A, 44B on the rotor R side (wherein T0 represents the time at locationX0, and T1 and T2 represent times at locations X1 and X2 respectively).

Next, an electrostatic motor according to the second embodiment of thepresent invention will be described.

FIG. 8 shows a vertical section of an electrostatic motor according tothe second embodiment. In FIG. 8, elements identical to those in theillustrations of the first embodiment are labeled with the same symbolsand duplicate explanation of these elements is avoided.

In the second embodiment, three rows of first electrodes 34A and threerows of second electrodes 34B are disposed along the circumferences ofelectrode supports 31, 32 respectively, on the stator S side. Similarly,two rows of first electrodes 44A and two rows of second electrodes 44Bare disposed along the circumferences of electrode supports 41, 42respectively. In the second embodiment, an electrostatic motor with ahigh output is produced by increasing the number of electrodes.

Next, an electrostatic motor according to the third embodiment of thepresent invention will be described.

FIG. 9 shows a vertical section of the electrostatic motor according tothe third embodiment. In FIG. 9, elements identical to those in theillustrations of the first embodiment are labeled with the same symbolsand duplicate explanation of these elements is avoided. The encoder, theslip rings, and the brushes are not shown.

In the first and second embodiments, limitations resulting from acantilever structure impede any unnecessary increase in electrodelength. In the third embodiment, first electrodes 44A are extended fromboth sides of each of electrode supports 41 on the rotor R side, andsecond electrodes 44B are also extended from both sides of each ofelectrode supports 42 on the rotor R side. This allows an output that istwice as high as that of an electrostatic motor with cantileverstructured electrodes in the first embodiment. In addition, the firstand second electrodes 34A, 34B may be extended from both sides of theelectrode supports 31 and 32, respectively, on the stator S side, andthe rotors R and stators S may be stacked in more than one stage in anaxial direction.

Next, an electrostatic motor according to the fourth embodiment of thepresent invention will be described.

FIG. 10 shows a vertical section of the electrostatic motor according tothe fourth embodiment, in which first and second electrodes on thestator side and first and second electrodes on the rotor side areradially arranged with respect to the center of the rotating shaft.FIGS. 11, 12 show vertical section of the stator and rotor,respectively, according to the fourth embodiment. Also in FIGS. 10 to12, elements identical to those in illustrations of the first embodimentare labeled with the same symbols and duplicate explanation of theseelements is avoided. The encoder, the slip rings, and the brushes arenot shown.

However, in the fourth embodiment, the positional relations between theelectrode supports 31, 32, insulator 33, first and second electrodes34A, 34B on the stator S side, and the electrode supports 41, 42,insulator 43, and first and second electrodes 44A, 44B on the rotor Rside, differ from those in the first to third embodiments.

In the fourth embodiment, first electrodes 44A are passed through thecomparatively large holes of a pipe-like electrode support 41, thenfirmly inserted, toward the axis, into the pipe-like electrode support42 with many holes, and thus fixed in position. Second electrodes 44Bare fixed to the electrode support 41. Similarly, first and secondelectrodes 34A, 34B are fixed to the electrode supports 31, 32,respectively, along the axis. The electrode supports 31, 32 are fixed toa motor base 10 or the body of a vacuum container 11 via the insulator33. The electrode supports 41, 42 are connected to a rotating body 12and a rotating shaft 1 via an insulator 43.

The configuration in the fourth embodiment ensures effects as excellentas those in the first to third embodiments.

1-9. (canceled)
 10. An electrostatic motor comprising: a containerhaving a main body; a stator which is fixed to the main body in thecontainer; and a rotor which is disposed opposite to the stator in thecontainer, and which is pivotally supported so as to freely rotate via arotating shaft, wherein the stator has first electrodes attached to afirst electrode support and second electrodes attached to a secondelectrode support, the first electrodes and the second electrodes areelectrically insulated, the rotor has third electrodes attached to athird electrode support and fourth electrodes attached to a fourthelectrode support, and the third electrodes and the fourth electrodesare electrically insulated, and the third electrodes and the fourthelectrodes are respectively arranged at different positions from thefirst electrodes and the second electrodes in a radial direction of therotor so as to be spaced apart from the first electrodes and the secondelectrodes.
 11. The electrostatic motor according to claim 10, whereinthe first electrodes and the second electrodes are each arranged in twoor more rows, and the third electrodes and the fourth electrodes areeach arranged intermediately between the rows of the first electrodesand the second electrodes.
 12. The electrostatic motor according toclaim 10, wherein predetermined electric fields are applied between thefirst electrodes and the second electrodes, and voltages of differentpolarities are applied to the third electrodes and the fourth electrodesso as to be switched at a predetermined timing.
 13. The electrostaticmotor according to claim 10, wherein the first electrodes, the secondelectrodes, the third electrodes and the fourth electrodes are eachrod-shaped and protrude in a direction parallel to an axial direction ofthe rotating shaft.
 14. The electrostatic motor according to claim 10,wherein the first electrodes, the second electrodes, the thirdelectrodes and the fourth electrodes have round ends.
 15. Theelectrostatic motor according to claim 10, wherein the first electrodesupport and the second electrode support are supported by an insulator,and at least one groove is formed on an outer periphery of theinsulator.
 16. The electrostatic motor according to claim 10, whereinthe third electrode support and the fourth electrode support aresupported by an insulator, and at least one groove is formed on an outerperiphery of the insulator.
 17. The electrostatic motor according toclaim 10, further comprising: another stator arranged in the container.18. The electrostatic motor according to claim 17, wherein the rotor isarranged between the stator and the other stator.
 19. The electrostaticmotor according to claim 10, further comprising: another rotor arrangedin the container.
 20. An electrostatic motor comprising: a containerhaving a main body; a stator which is fixed to the main body in thecontainer; and a rotor which is disposed opposite to the stator in thecontainer, and which is pivotally supported so as to freely rotate via arotating shaft, wherein the stator has first electrodes attached to afirst electrode support and second electrodes attached to a secondelectrode support, the first electrodes and the second electrodes areelectrically insulated, the rotor has third electrodes attached to athird electrode support and fourth electrodes attached to a fourthelectrode support, and the third electrodes and the fourth electrodesare electrically insulated, and the third electrodes and the fourthelectrodes are respectively arranged at different positions from thefirst electrodes and the second electrodes in a direction parallel to anaxial direction of the rotating shaft so as to be spaced apart from thefirst electrodes and the second electrodes.
 21. The electrostatic motoraccording to claim 20, wherein the first electrodes and the secondelectrodes are each arranged in two or more rows, and the thirdelectrodes and the fourth electrodes are each arranged intermediatelybetween the rows of the first electrodes and the second electrodes. 22.The electrostatic motor according to claim 20, wherein predeterminedelectric fields are applied between the first electrodes and the secondelectrodes, and voltages of different polarities are applied to thethird electrodes and the fourth electrodes so as to be switched at apredetermined timing.
 23. The electrostatic motor according to claim 20,wherein the first electrodes, the second electrodes, the thirdelectrodes and the fourth electrodes are each rod-shaped and protrude ina radial direction of the rotor.
 24. The electrostatic motor accordingto claim 23, wherein the first electrodes protrude toward the rotorthrough holes which are formed in the second electrode support.
 25. Theelectrostatic motor according to claim 23, wherein the fourth electrodesprotrude toward the stator through holes which are formed in the thirdelectrode support.